Shadows on ST -i guide camera image using OAG 8300

Discussion in 'Specialty Cameras SG-4, AllSky, ST-I' started by James Mok, Dec 21, 2018.

  1. James Mok

    James Mok Standard User

    Dec 21, 2018
    I have recently purchased a STF-8300 kit with FW8 and OAG 8300/ST-i. Initially I got shadows on my STF-8300 images but I managed to get rid of them after adjustment of the pickoff mirror (prism). However, the image from the guide camera (ST-i) has almost 1/3 covered with a shadow no matter I adjusted the prism. This shadow does not rotate even if I rotate the connection of STF-8300 to the scope so I suppose it has something to do with the OAG setup. Attached is an image from ST-i attaching to the OAG in daytime showing the shadow on the left side. This shadow would rotate if I rotate the ST-i but still occupies a large area. Please let me know if there is normal or anything else I should try to adjust.

    Attached Files:

    • OAG.JPG
      File size:
      221.6 KB
  2. Doug

    Doug Staff Member

    Sep 25, 2014
    That is probably vignetting from your optical system. If the illuminated circle from the telescope is small then the pick-off position is a compromise between shadowing the main camera and vignetting the guider.

    It may also be possible to vignette the image within the OAG if it is not adjusted properly.

    Make sure the pick-off is on the long, narrower side of the main sensor. Move it in until it almost shadows the main chip.

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